What Is Soil? Soils-1-1 Image: T. Loynachan

Soil is a layer of unconsolidated material on the Earth’s surface in which plants grow. Soils-1-2 Image: Louis Maher Image: Professional Soil Classifiers Assoc. of Alabama

Soil is a mixture of mineral grains from the Earth, decomposing organic matter, and voids filled with air or water. Soils-1-3 Image: Professional Soil Classifiers Assoc. of Alabama

Soil is the Earth material that links living things (biosphere), air (atmosphere), water (hydrosphere), and the solid Earth (geosphere). Soils-1-4 Image: Bruce Molnia

A soil profile is an exposure from the surface downward through a soil to its parent material. Soils-3-1 Image: NRCS Image: Martin Miller

Soil profiles generally expose three layers or soil horizons. Soils-3-2 Image: National Cooperative Soil Survey

The upper “A” horizon contains organic matter mixed with mineral particles. Percolating water dissolves and removes some mineral constituents from the “A” horizon. Horizon “A” Soils-3-3

Some constituents dissolved from the “A” horizon are deposited below in the “B” horizon. Horizon “A” Horizon “B” Soils-3-4

The “C” horizon is the lower soil layer developed on the underlying parent material. Horizon “A” Horizon “B” Horizon “C” Soils-3-5

A mature soil profile with well developed A, B, and C horizons takes hundreds to thousands of years to develop. Horizon “A” Horizon “B” Horizon “C” Soils-3-6 Image: NRCS

Physical weathering breaks rocks into small mineral particles that accumulate on the Earth’s surface. Soils-2-2 Images: Martin Miller, NRCS

How Soils Form Soils-2-1 Image: T. Loynachan

Chemical weathering dissolves and changes minerals that have accumulated on the Earth’s surface. Soils-2-3 Images: National Cooperative Soil Survey, University of Nebraska

Decomposing organic material from plants and animals mixes with accumulated soil minerals. Soils-2-4 Images: NRCS, Soil Classifiers of Michigan

Accumulated soil materials contain voids filled with air or water. Soils-2-5 Image: T. Loynachan

Continued physical and chemical changes over hundreds to thousands of years produce layers called soil horizons. Soils-2-6 Image: National Cooperative Soil Survey